I bound off the collar last night, prematurely, to get a sense of how it was laying. The cardigan still needs sleeves, obviously, but here's what it looks like with the shoulders grafted, the bottom border re-knit, and half the collar:
Mountain Man commented that I could just stop here and wear it as a vest. I'm tempted to follow the suggestion, as I'm getting tired of the project and am dreading the process of adjusting the sleeve caps to fit my armscye modifications. Also, it's pushing 80 degrees, and a wool/mohair cardigan seem rather unseasonable.
BUT. sigh. I don't like the flare of the button band.
The extra volume of the garter stitch makes sense around the neck, as it's supposed to be able to fold over into a shawl collar. But, down at the bottom, it ends up making waist-coat points, which are really not my thing.
This aspect didn't seem so noticeable in all the other versions I saw on Ravelry; maybe once you've got the full width of the collar, with more overlap of the sides, the points aren't so pronounced. Or maybe .... gulp .... I've got to re-knit the collar with fewer stitches picked up at the bottom! Stay tuned ...